Method for Detecting a Duplicate Address, Mobile Station, Network Element and Communication System

1. A method for detecting a duplicate address, wherein a mobile station is moving from a second access network pertaining to a second network element into a first access network pertaining to a first network element, comprising: receiving, by the first network element, a request message from the mobile station; sending, by the first network element, a first message to the mobile station upon reception of said request message, said first message designating an explicit address configuration and including prefix information; receiving, by the first network element, a message containing an address generated based on said prefix information by the mobile station, the mobile station presuming the generated address is a valid address, the message indicating that the mobile station requires registration of the generated address with the first network element without the first network element waiting for confirmation on a uniqueness of the generated address from other network elements, which has been presumed a valid address by the mobile station; and creating, by the first network element, an entry for the mobile station if the generated address is not found in its address table without waiting for the confirmation on the uniqueness of the generated address from the other network elements, or generating a second message and sending the second message to the mobile station for indicating that the generated address is a duplicate address if it is found in its address table and discarding data packets with the duplicate address sent from the mobile station.

2. The method according to claim 1 , wherein the mobile station performs one or more of the followings operations: regenerating a new address and repeats those steps of claim 1 upon reception of said second message for indicating that the generated address is a duplicate address; sending a message for de-registering the generated address with the first network element when it is about to leave the first access network or stop using the generated address; and setting the first network element as its default gateway while generating said address based on said prefix information.

3. The method according to claim 1 , wherein said entry is invalid after its lifetime expires if the first network element does not receive from the mobile station a message for deregistering the generated address with the first network element.

4. The method according to claim 1 , wherein said entry contains a care of address and a corresponding link-layer address of the mobile station, and/or check-up of a message includes check-up of a specific field of the message.

5. The method according to claim 1 , wherein the first network element deletes said entry if a match between the generated address and its address table is found, upon receiving from the mobile station said message for de-registering, or ignore said message for de-registering if no match is found.

6. The method according to claim 1 , wherein said address table includes an IP address, a link-layer address of the mobile station and a life time of the addresses, and/or said address is a stateless address.

7. A mobile station moving from a second access network pertaining to a second network element into a first access network pertaining to a first network element, comprising: first message generation means for generating a request message and sending the request message to the first network element; first message check-up means for checking a message sent by the first network element in response to the request message, to find if an explicit address configuration is required; second message generation means for generating a message for indicating that the mobile station requires registering an address generated by itself with the first network element without the first network element waiting for confirmation on a uniqueness of the generated address from other network elements, or for indicating that the mobile station requires de-registering the generated address with the first network element when it is about to leave the first access network or stop using the generated address; and second message check-up means for checking a message sent by the first network element to find if the generated address which has been presumed a valid address by the mobile station has been subsequently determined by the first network to be a duplicate address.

8. The mobile station according to claim 7 , wherein the mobile station abandons the generated address and regenerates a new address when a duplicate address is detected by the first network element, and/or said address is a stateless address.

9. The mobile station according to claim 7 , wherein checking the message includes check-up of a specific field of the message.

10. A network element for controlling access of a mobile station to a wide area network, wherein the mobile station is moving from a second access network pertaining to a second network element into a first access network pertaining to a first network element, comprising: message receiving means for receiving a request message from the mobile station; first message generation means for generating a message, in response to receiving the request message, for designating an explicit address configuration and including prefix information; message check-up means for checking a message sent by the mobile station to find whether the mobile station requires registration of an address generated by itself without the network element waiting for confirmation on a uniqueness of the address from other network elements or requires de-registering the generated address; an address table adapted to store an IP address and a link-layer address of the mobile station, as well as life time of the addresses; address lookup means for looking up the address table for an address generated by the mobile station which has been presumed a valid address by the mobile station; entry creation means for creating an entry for the mobile station if the generated address is not found in the address table; second message generation means for generating a message for indicating that the generated address, which the mobile station is presently using as an identification, is a duplicate address; and packet discarding means for discarding data packets with the duplicate address sent from the mobile station.

11. The network element according to claim 10 , further comprising: entry deleting means for deleting the entry when the mobile station requires deregistering the generated address and the generated address is found in said address table.

12. The network element according to claim 10 , wherein said entry is invalid after its lifetime expires if the network element does not receive from the mobile station said message for deregistering the generated address.

13. The network element according to claim 10 , wherein said entry contains a care of address and a corresponding link-layer address of the mobile station.

14. The network element according to claim 10 , wherein the checking the message includes a check-up of a specific field of the message, and/or said address is a stateless address.